1. Field of the Invention
This invention relates to a continuous filter press, and more specifically, to a continuous dual functional filter for the slurry fed under pressure which also scrapes the cake piled on the filter medium, compresses and discharges the precipitated cakes continuously.
2. Description of the Prior Art
Prior arts of the pressure filters are all not continuous but batch types, such as the conventional filter press, leaf filter, tubular filter and etc. Inevitable defects they have;
(a) To take filtered cakes out of filter, the filter has to be opened up, causing to emit the solvent vapor or the order in the open. PA1 (b) The drawn out cakes, mostly mixed with the remaining slurry, have to be removed by hands or transferred often in the open by the conveyer. PA1 (c) At least a worker is needed for its operation, even of the complete automatic type. PA1 (d) Skillful alignment of the filter medium to the frame, is necessary to prevent the slurry leak. PA1 a filtering zone comprising a filter medium, and a filtrate-collecting chamber and a chamber for containing a slurry and a filtered cake; PA1 a cake-compressing conical zone connected at one end of the filter chamber, where a rotating screw squeezes and moves downward falling cakes scraped end puled off from the filter zone; PA1 a cake-discharging zone connected to the other end of the cake-compressing zone for discharging a compressed cake formed in the cake-compressing zone; PA1 a slurry feed opening and closing valve arranged on the slurry feed mechanism; PA1 a cake discharge control mechanism for detecting the cake-compressing degree in the cake-compressing zone and opening or closing the cake-discharging zone to control the discharge of the compressed cake; PA1 a backwashing mechanism for peeling off the heel cake and washing the filter medium; PA1 a slurry relief conduit and valve, for decreasing immediately the pressure in the filter chamber; PA1 a detecting mechanism of clogging up of the filter medium, such as checking the flow rate of the filtrate and measuring the pressure difference between the filter zone and the filtrate collecting chamber; PA1 a control mechanism with an aid of the above detecting mechanism, of shutting the slurry feed, introducing the backwashing fluid to the filtrate collecting chamber and opening the relief valve to lessen the pressure in the filter chamber at least once during the backwashing period, thus enabling to clean the filter medium in a very short time and at the same time collecting the peeled off cakes in the compression zone.
A screw press is exceptionally continuous, however it has a fundamental defect that is originated in its performance to filter the slurry as well to compress its cake with all mechanical force by pushing them against the perforated metallic cylinder with large diameter holes such as one to several milimeter.
Inevitably the filtrate through the perforated cylindrical drum, carries along considerable amount of constituent solid particles.
Moreover, the discharge of the compressed cake is done through the blocking plate, which accompanied various inconveniences in operation and gives unfavorable effect to the extent of the cake compression.
In order to improve the above shortcomings, U.S. Pat. No. 4,464,253, GB Patent No. 2119670 and Japanese Patent Publication No. 4324/90 were applied. Applying the above patent for the filtration of slurries having coarse, as much as say 30.mu. or like and hard particles, for example a slurry having active carbon particles, has been successful in continuous operation for long time, say successive 7 days or more, with keeping a constant cake thickness and holding a constant filtration rate by scraping the cake.
However, the viscous slurries having fine as small as, say a few microns or like and soft particles, for example Al(OH).sub.3 and etc., are likely to plug up the heel cake far sooner than the former slurry, which necessitates to peel the heel cake off and to clean the filter medium prior to complete plug up.
The invention is an enclosed continuous filter press, accompanying automatic back washing devices to peel off the heel cake, to clean the filter medium and at the same time recover cakes in a compressed state, all in enclosure and in a very short time, to function as an almost continuous filter press in enclosure, which reducing the loss time as much as possible.